This invention was made in the course of, or under, a contract with the Energy Research and Development Administration. This invention relates to the art of separating mono-octylphenyl and di-octylphenyl esters of phosphoric acid and more particularly to a solid/liquid separation process where the mono-octylphenyl phosphoric acid ester is separated and recovered from the solid phase.
The separation process of this invention is particularly useful for providing a substantially pure mono-octylphenyl phosphoric acid ester for use as a make-up component for the extractant in a process for recovering uranium from wet-process phosphoric acid. Such a process is more fully described in commonly assigned U.S. Pat. No. 3,835,214 issued Sept. 10, 1974 to Hurst et al. for "Oxidative Stripping Process for the Recovery of Uranium from Wet-Process Phosphoric Acid" the disclosure of which is incorporated herein in its entirety by reference.
In the Hurst et al. process, uranium values present in the feed solution (5 to 6 M H.sub.3 PO.sub.4) are concentrated in a first cycle by a factor of 70 to 100 by extracting into an organic phase (typically a mixture of mono- and di-octylphenyl esters of orthophosphoric acid dissolved in an inert diluent) and stripping from the organic phase into an 8 to 12 M H.sub.3 PO.sub.4 solution containing an oxidizing agent. During the course of operation of the Hurst et al. process, the first cycle extractant which is continuously recycled becomes depleted in the mono-octylphenyl ester due to its slight solubility in the aqueous H.sub.3 PO.sub.4 solution.
It has been found that the efficiency of the first cycle extraction is somewhat dependent upon the ratio of mono- to diester in the extractant. The commercially available octylphenyl phosphoric acid ester is approximately a 1 to 1 molar ratio of the mono- and di-esters. Satisfactory extraction efficiency is attainable with a molar ratio of mono- to di-ester in the range of from about 1-1 to about 1-7. If the first cycle extractant becomes more depleted in the mono-ester, the extractive efficiency diminishes rapidly. In order to maintain the preferred mono- to di-ester ratio, either the first cycle extractant must be periodically renewed or a separated mono-ester must be periodically added to the recycled extractants as a make-up component.